Field of the Invention
The invention relates to a method of manufacture of a functional element, especially a stent, as well as to the use of a salt bath for heat treatment of an intravascular functional element. The invention also relates to an intravascular functional element, especially a stent.
Discussion of the Background of the Invention
In medical technology, stents are usually produced by laser methods. However, braids of Nitinol wires are also used for implants (e.g. stents or occluders). In contrast to stents produced by laser methods, the wires of wire braids slide over one another and therefore permit good shape adaptation of the stent structures. In principle, (vascular) implants may be manufactured from semifinished materials such as sheet, precision tubes or wires.
For example, US 2004/0117001 A1 describes a method of manufacture of a stent from Nitinol. One objective of US 2004/0117001 A1 consists in reducing the nickel content in a near-surface layer in order to prevent nickel from being released from the layer, since thereby the biocompatibility of the stent is impaired. A laser method is proposed for production of the stent. After a cold-working step, the stent is heat-treated and then electropolished at temperatures below 20° C. For thermal oxidation, the stent is exposed to superheated steam at a temperature of 150° C. for 12 h. Thereby an oxidic surface with an Ni content of less than 2 wt % in a layer depth of 10 nm is supposedly obtainable.
The known method has the disadvantage that the oxide layer that can be produced therewith on implants consisting of wire braids wears rapidly. For braids, it is important that the contact surfaces of the wires touching one another have low friction, precisely considering that the implanted braids are continuously exposed to pulsatile vessel movements and the wires therefore move relative to one another. Above and beyond this, a low coefficient of friction of the wire surfaces is important for good mobility of the implant in an introducing catheter.
One object of the invention is to propose a method with which an intravascular functional element, especially a stent or intravascular coil or intravascular occlusion device can be produced with improved wear and friction properties and good biocompatibility. Another object of the invention is to provide an intravascular functional element, especially a stent or intravascular coil or intravascular occlusion device with improved wear and friction properties and good biocompatibility. A further object of the invention is to propose the use of a salt bath for heat treatment of an intravascular functional element.